OfType

OfType is a LINQ operator that filters elements of a sequence, returning only those that are of a specified type. It is defined for both enumerable sequences (Enumerable.OfType<TResult>) and queryable sequences (Queryable.OfType<TResult>).

Behavior and return value: For each element in the source sequence, OfType tests whether the element can be cast to the specified type TResult. If the cast succeeds, the element is yielded as TResult; otherwise the element is skipped. The operation uses deferred execution, meaning elements are evaluated as the resulting sequence is enumerated. The result is an IEnumerable<TResult> for Enumerable.OfType and an IQueryable<TResult> for Queryable.OfType.

Difference from Cast: Cast<T> attempts to cast every element in the source sequence to T and will throw an exception if any element cannot be cast. OfType<T>, by contrast, filters out elements that cannot be cast, returning only those that match the type.

Usage and examples: Commonly used to extract elements of a specific type from a heterogeneous collection. For example, object[] items = { 1, "two", 3.0, "four" }; var strings = items.OfType<string>(); // yields "two" and "four"

Query translation: When used with IQueryable sources, OfType<TResult> translates into a type-check operation that can be executed by the underlying query provider. Most LINQ providers support it, though translation details may vary.

Notes: OfType is useful for selecting elements of a given type without requiring an explicit cast on the entire sequence. It is a standard, widely supported part of the LINQ set of operators.